Instrument panels, or clusters, are commonly found in a variety of vehicles and in industrial equipment. Often the instruments in those panels provide information about the condition or behavior of a system and its components, where the information is typically derived from remotely located sensors. One such instrument is an analog gauge composed of a gauge pointer that moves relative to some indicative scale. An example of such a scale is the fuel gauge; label “E” indicates empty, and various other labels indicate other states of fuel levels, such as “¼,” “½,” “¾,” as well as “F” for full. Conventional gauge pointers generally use a rotational motor to position the pointer to reflect a condition of the system being indicated. The rotational motors of present-day art consist mainly of air-core motors and stepper motors. Although these motors are commonplace, their form-factor and weight represent obstacles in progressing toward lighter, thinner, and better illuminated gauges. Such attributes are particularly desirable for automotive applications where weight and thickness savings have cost and environmental benefits, and where improved indicator visibility may result in increased passenger safety.
The thermoelastic properties of shape memory alloys (SMA) have been known since the 1930s, but commercially viable uses for SMAs were not widespread until the 1990s. Today, SMAs are finding unique applications in a variety of industries. One such application is an SMA-actuated gauge pointer, which is described in U.S. Pat. No. 6,441,746 to Taborisskiy et al. But the pointer mechanism proposed by Taborisskiy requires a cumbersome gearing mechanism within a large footprint, much like previously known stepper motor-actuated pointers. Further, Taborisskiy's proposed gauge mechanism lacks thermal compensation for the SMA element and thus is generally sensitive to environmental temperature swings. Without a compensation mechanism, Taborisskiy's gauge mechanism is generally prone to conveying unreliable measurements.
In view of the foregoing, what is needed is an improved rotary actuator, and more specifically, an improved SMA-actuated gauge pointer to overcome these and other shortcomings in existing instrument devices, such as gauge pointer actuators.